Antihardeners for polymers

ABSTRACT

Amide age resisters such as N-(4-anilinophenyl) acrylamide and methacrylamide are added to certain diene polymers such as SBR, NBR and natural rubber prior to compounding with reinforcing agents such as carbon black, thereby improving the hardening resistance of the subsequently sulfur vulcanized polymer.

United States Patent Maxey Feb. 18, 1975 ANTIHARDENERS FOR POLYMERS 3,658,769 4/1972 Kline 260/83,?

[75] Inventor: Frank S. Maxey, Uniontown, Ohio [73] Assignee: The Goodyear Tire & Rubber Primary Examiner MelvYn L Marquis Company, Akron Ohio Assistant Examiner-H. H. Fletcher, Attorney, Agent, or FirmF. W. Brunner; J. A. [22] Filed: Jan. 30, 1974 Rozmajzl [21] Appl. No.: 438,055

52 US. Cl 260/4232, 260/4237, 260/4247, [571 ABSTRACT 260/4248, 260/4252, 260/459 NC, 260/833 260/851, 260/562 P, 260/801 Arnlde age resisters sucb as N-(4-anilmopheny l) aeryl- [51] Int CL cosc 11/10 C08C 11/18 cogc 11/46 amide and methacrylamide are added to certain diene [58] Field of'search 360/45 9 801 562 P polymers such as SBR, NBR and natural rubber prior 42 42 85 to compounding with reinforcing agents such as carbon black, thereby improving the hardening resistance [56] References Cited of the subsequently sulfur vulcanized polymer.

UNITED STATES PATENTS 10 Claims, N0 Drawings 3,576,003 4/1971 Strobel et a] 260/459 NC ANTIHARDENERS FOR POLYMERS This invention relates to reinforced diene vulcanizates which are resistant to hardening. More particularly, this invention relates to a process of improving the resistance of certain loaded diene rubber vulcanizates to hardening.

Various diene rubber vulcanizates have been known to harden while being stored or used at elevated temperatures. The hardening can be due to changes in the crosslink structure of the polymer, resinification or cyclization of the polymer or bridging of the polymer chains. Hardening can cause tire treads to crack or chunk, hoses to split, gaskets to fail to seal properly and belt covers to crack. lt'will manifest itself as an increase in hardness, an increase in modulus, a decrease in elongation and sometimes as a decrease in tensile.

[t is an object of the present invention to provide a process for improving the resistance of certain reinforced diene rubber vulcanizates to hardening. It is also an object of the present invention to provide unvulcanized reinforced rubber compositions which can be vulcanized into reinforced rubber vulcanizates which are resistant to hardening. Other objects will become apparent as the description proceeds.

The objects of the present invention are accomplished by adding an amide to the vulcanized diene rubber prior to the addition of a substantial amount of the reinforcing agent.

The amide has the following structural formula: 30

NH NH C C HC R H I i wherein R, R R and R are selected from the group consisting of hydrogen and alkyl radicals having from 1 to 4 carbon atoms, wherein R and R can also be alkoxy radicals having 1 to 4 carbon atoms, and wherein R is selected from the group consisting of hydrogen, alkyl radicals having from 1 to 4 carbon atoms, aryl radicals having from 6 to 12 carbon atoms, aralkyl radicals having from 7 to 13 carbon atoms, cycloalkyl radicals having from 5 to 12 carbon atoms atoms, carboxymethyl radicals and carbalkoxy methyl radicals and wherein R is selected from the group consisting of hydrogen, alkyl radicals having from 1 to 4 carbon atoms, aryl radicals having from 6 to 12 carbon atoms, cycloalkyl radicals having from 5 to 12 carbon atoms, carboxy radicals and carbalkoxy radicals.

The carbalkoxy methyl radicals preferably have the following structural formula wherein R is an alkyl radical having from 1 to 4 carbon atoms. Preferably the carbalkoxy radicals have the following structural formula f-c-o-R wherein R is an alkyl radical having from i to 4 carbon atoms.

Preferably R, R R and R are selected from the group consisting of hydrogen and methyl. Preferably R is selected from the group consisting of hydrogen and methyl. Preferably R is hydrogen. Preferably R and R are selected from the group consisting of methyl and ethyl.

Representative amides which can be used in'the practice of the present invention include the following. N-(4'anilinophenyl) acrylamide N-(4-anilinophenyl) methacrylamide N-(4-anilinophenyl) cinnamamide N-(4-anilinophenyl) crotonamide N-[4-(4-methylanilino)phenyl] acrylamide N-[4-(4-methylanilino)phenyl] methacrylamide N-[4-(4-methoxyanilino)phenyl] acrylamide N-[4-(4-methoxyanilino)phenyl] methacrylamide N-[4-(4-ethoxyanilino)phenyl] acrylamide N-[4-(4-ethoxyanilino)phenyl] methacrylamide N-[4-(4-N,N-dimethylaminoanilino)phenyl] acrylamide N-(4-anilinophenyl) maleamic acid N-(4-anilinophenyl) itaconamic acid N-[4-(4-methylanilino)phenyl] maleamic acid N-(-anilinophenyl) citraconamic acid The method of preparing the amides is not critical to the performance of these compounds in the practice of the present invention.

The amides can be prepared by reacting normally in substantially molar amounts an amine of the structure NH EH with an acid halide of the structure ac c c Ix I I It R a o m where R, R R and R are as defined earlier herein and wherein X is selected from the group consisting of chloride and bromide radicals, in the presence of an acid absorbing agent which may be an inorganic salt, e.g., sodium carbonate, or an organic tertiary amine. e.g., triethylamine. The reaction is usually carried out by dropwise addition of a solution of the acid halide in an aprotic solvent to a solution of the amine which contains in solution or in suspension 21 compound capable of reacting with the hydrogen halide formed during the reaction. A slight excess of acid halide may be used. The reaction is usually exothermic so the temperature during reaction is held to a maximum of 50 C. by means of an ice water bath. The reaction mixture is stirred for an hour or more after the addition of acid halide has been completed. The product usually precipitates during the course of the reaction. It is then filtered off, dried, and purified as necessary.

Examples of amines which can be used in preparing the amides are as follows.

4-aminodiphenylamine 4-amino-4-methyl diphenylamine 4-amino-4 -methoxy diphenylamine 4-aniino-4'-ethoxy diphenylamine 4-amino-4-(N,N-dimethy1amine) diphenylamine 4-amino-4'-isopropyl diphenylamine The level of antioxidant which can be used effectively in the practice of the present invention should It has been discovered that time of addition of the amide is critical if antihardening improvements are to be obtained. If the amide is added after the reinforcing agent is added. the vulcanized polymer will have a greater tendency to harden on aging. If the amide is added prior to the addition of the reinforcing agent. the vulcanizate will be more resistant to hardening. The larger the amount of the reinforcing agent added prior to the amide addition, the greater is the tendency of the vuleanizate to harden. The amide therefore must be ,added before all of the reinforcing agent has been added. Preferably the amide is added before half of the reinforcing agent is added. More preferably the amide is added before a third or even a quarter of the reingenerally not be less than 0.25 part p r 100 parts b forcing agent has been added. That is to say that the weight of uncompounded diene rubber. Preferably the level is at least 0.5 part. The upper level of amide antioxidant that can be used is 5.0 parts and higher. Preferably, however, the upper level will not exceed 2.0 parts. A preferred range of antioxidant is from 1.0 part to 1.5 parts.

Examples 1, 2, 5 and 6 in U.S. Pat. No. 3,658,769 illustrate the preparation of compounds of the present invention and are incorporated herein by reference.

The amides of the present invention can be used alone or in combination. They are added to the diene rubber prior to the addition of the reinforcing agent.

A reinforcing agent interacts with the rubber to increase the modulus and hardness of the rubber. Typical well known reinforcing agents are the carbon blacks (such as HAF, SAF,1SAF, SRF, FEF and GPE blacks) and silicas such as precipitated fine particle size hydrated amorphous silicas and fumed silicas (nonhydrated). Other non-black reinforcing agents are calamide is added before a substantial amount of reinforcing agent is added. Most preferably the amide is added before any of the reinforcing agent is added. As a guideline, the polymer to which the amide is added 0 should normally contain less than 30 parts by weight of reinforcing agent per 100 parts by weight of polymer when the amide is added, preferably less than 20 parts and most preferably less than 10 parts. The remainder or all of the reinforcing agent is then added.

A 67/33 butadiene/acrylonitrile rubber (NBR) was compounded as indicated in the following table. Examples 1 and 2 were compounded and vulcanized using one type of a vulcanization system while Examples 3 and 4 were compounded and vulcanized using another vulcanization system. In Examples I and 3. N-(4- anilinophenyl) methacrylamide was added prior to the addition of carbon black. 1n Examples 2 and 4 the methacrylamide was added with carbon black in the Banbury. The compounded rubbers were vulcanized at optimum times and temperatures, and then aged for various times at various temperatures. The aged tensiles (meganeutons) and elongations (percent) were -measured. The tensile x elongation products are shown 7 in the following table.

TABLE 1 Examples 1 2 3 4 NBR 100 N-(4-anilinophenyl) methacrylamide 1 Carbon black Stearic acid 1 Oil 5 Amine antioxidant 1 Magnesium oxide 5 5 Zinc oxide 3 3 Benzothiazyl disulfide 1.5 1.5 Cadmium oxide 2.0 2.0 Cadmium diethyl dithiocarbamate 2.5 2.5 2-(morpholinodithio )-benzothiazo 1e 1.5 1.5 Tetramethyl thiuram disulfide 2.0 2.0 2-(morpho1inothio )-benzothiazo1e 1. 1.5 Sulfur 0.3 0.3 Vulcanization (min. at 150C.) 10 1 l 27 30 Tensile X Elongation X 10 Original 4.8 4.9 10.4 1 1.0 hours at 121C. 3.9 3.7 8.3 7.1 7 days at 121C. 2.6 2.3 5.3 4.4 14 days at 121C. .33 .28 3.4 1.5 70 hours at C. .14 .8 4.5 1.2 70 hours ASTM No. 30:1 at 150C. 4.0 4.4 9.8 8.5 7 days ASTM No. 30:1 at 150C. 3.11 3.2 0.5 7.5 14 days ASTM No. 30:1 at 150T. 2.) 2.5 $4.0 (.1

Examples 1 and 3 represent the practice of the present invention, i.e., the addition of the amide prior to the addition of the reinforcing agent. The aging results with Examples 1 and 3 were superior to those obtained with 2 and 4 respectively. It will be noted that the order of addition was more critical with the vulcanization system used in Examples 3 and 4. This illustrates the fact that the order of addition is more critical with the more efficient vulcanization (EV) systems such as the system of Examples 3 and 4.

It should be noted that the present invention does not benefit low efficiency vulcanization systems. The systems which benefit are the efficient and semi-efficient vulcanization systems which are well known in the art. Such systems are described in the two articles appearing in Rubber Age, the November and December issue of 1967, the articles being entitled EV Systems For NR-Part l and EV Systems for NR-Part 2, as well as in the Natural Rubber Technical Information Sheets Nos. 118 and 119, published by the Natural Rubber producers Research Association. EV and semi-EV systems are characterized by the fact that they provide a large number of sulfur crosslinks for a given amount of sulfur. whether added as free sulfur or resulting from a sulfur donor, i.e., a compound capable of providing sulfur such as tetramethyl thiuram disulfide or 2- (morpholinodithio)-bcnzothiazole. Normally a low level of sulfur is used, for example 0.7 part by weight per 100 parts by weight of polymer and even a 0.5 part and below. In fact, sulfurless systems using sulfur donors are particularly efficient systems (note Examples 3 and 4 above). The-object of an efficient or semiefficient system is to provide as many monosulfidic crosslinks as possible and as few cyclic sulfide groups as possible.

In Examples 5, 6, 7, 8 and 9 N-(4-anilinophenyl) methaerylamide was added to an SBR stock before any carbon black was added and after various amounts of carbon black were added. Again the samples were vulcanized and aged. The compounding recipe and test results are shown below.

TABLE ll Silica-type reinforcing agents could have been substituted in the previous examples for the carbon black. and improvements based on order of addition would have been obtained.

Any of the conventional compounding techniques. e.g., banburying and milling, can be used.

The diene polymers which will benefit by the practice of the present invention are those polymers prepared from conjugated diene monomer. The diene polymer can be a homopolymer or a eopolymer of diene monomer and one or more comonomers. The eopolymer will contain at least parts by weight per 100 parts by weight of polymer of one or more segnieric forms of conjugated diene monomer, preferably at least parts and most preferably at least parts. Illustrative conjugated l,3-diene monomers are butadiene-l .3; isoprene; 2-chlorobutadiene; Z-ethyI-butadiene-l ,3; and 2,3- dimethyl butadiene-l,3. Copolymerizable monomers include vinyl and vinylidene monomers such as styrene, oz-methyl styrene, divinyl benzene, vinyl acetate, vinylidene chloride methylmethacrylate, ethylacrylate, the vinyl pyridines including 2-vinyl pyridine; 5-methyl-2- vinyl pyridine; 4-vinyl pyridine and 2-vinyl5-ethyl pyri dine; acrylonitrile, methacrylonitrile, methacrylic acid and acrylic acid. Mixtures of the diene monomers and mixtures of the comonomers can be used.

The term sulfur-type vulcanization system is intended to include free-sulfur or sulfur donor systems as well as combinations thereof.

Examples SBR I500 Zinc oxide Magnesium oxide Carbon black Stearie acid Oil N(4-anilinophenyl)melhacrylamide Tetramethyl thiuram disulfide 2-(morpholinodithio)-benzothiazole Oil-ts: I

2-( morpholinothio)-benzothiazole Vulcanization (min. at 150C.) Tensile Elongation X l0 Original 70 hours at l5()C. 7 days at l2l"Cv 14 days at l2lC.

" Added before addition of any carbon black.

after l5 parts of carbon black added.

' Added after 30 parts of carbon black added.

*" Added after 60 parts of carbon black added.

Added on mill with curatives after 60 parts of carbon black added.

Depending upon the type of aging, the addition of the methacrylamide before any of the carbon black was 6 added (Example 5), resulted in an aged tensile X elongation improvement of 15 to over the sample where all ofthe carbon black was added first (Example 8), thereby demonstrating the criticality of the order of addition.

therein without departing from the spirit or scope of the invention.

I claim: I V 2. The vulcanizate prepared by vulcanizing the un- I. In a process of preparing an unvulcanized conjuvulcanized conjugated diene polymer of claim 1 with gated dien polym r ontaining a r inforcing agen an efficient or semi-efficient sulfur-type vulcanization said polymer containing not more than 0.25 part by system.

weight per 100 parts by weight of an anti-hardener and The unvulcanized Conjugated diene polymer bemg capable of being vulcanized w th a sulfur-type pared according to the process of Claim 1. vulcanization system to form a vulcanizate, said vulcanizate having a tendency to harden, the improvement. wherein an amide, in the amount of at least 0.25 part by weight per 100 parts by weight of polymer, is added to the polymer before all of the reinforcing agent has diene is butadlene'l been added to the polymer with the proviso that the 6. The process of claim 5 wherein the polymer is a polymer contains less than 30 parts by weight of reincopolymer containing at least 40 parts by weight of forcing agent per 100 parts by weight ofpolymer when butadiene-l,3 per 100 parts by weight of polymer and the amide is added and wherein the amide has the folas a comonomer a monomer selected from the group 4. The process of claim 1 wherein the reinforcing agent is carbon black.

5. The process of claim 4 wherein the conjugated lowing structural formula: consisting of styrene and acrylonitrile.

NH NH c c HC a II I R R o R wherein R, R R and R" are selected from the group 7. The process according to claim 1 wherein the consisting of hydrogen and alkyl radicals having from amide is N-(fl-anilinophenyl)-methacrylamide. l to 4 f q wherein R5 and R6 can also be 8. The process according to claim 1 wherein the polyrad'cals havmg l to 4 Carbon a m and wherem mer contains less than parts by weight of reinforcing R is selected from the group consisting of hydrogen, agent per 100 parts by weight of polymer when the alkyl radicals having from 1 to 4 carbon atoms, aryl amide is added radicals having from 6 to 12 carbon atoms, aralkyl radicals having from 7 to 13 carbon atoms, cycloalkyl radi- 9. The process according to claim 1 wherein the polycals having from 5 to 12 carbon atoms carboxymethyl mer contains less than 10 parts by weight of reinforcing radicals and carbalkoxy methyl radicals and wherein R agent per 100 parts by weight of polymer when the is selected from the group consisting of hydrogen, alkyl' amide 18 edl g a 1 3 carbon atoms aryl radicals 10. The vulcanizate according to claim 2 wherein the having mm to car on atoms cycloalkyl radlcals vulcanization system contains 0 to 0.5 part by weight having fromSto 12 carbon atoms,carboxy radicals and ff If 100 t b W ht f carbalkoxy radicals. 40 O ree Su Ur per f, i 0 p0 ymcr' 

1. IN A PROCESS OF PREPARING AN UNVULCANIZED CONJUGATED DIENE POLYMER CONTAINING A REINFORCING AGENT, SAID POLYMER CONTAINING NOT MORE THAN 0.25 PART BY WEIGHT PER 100 PARTS BY WEIGHT OF AN ANTI-HARDENER AND BEING CAPABLE OF BEING VULCANIZED WITH A SULFUR-TYPE VULCANIZATION SYSTEM TO FORM A VULCANIZATE, SAID VULCANIZATE HAVING A TENDENCY TO HARDEN, THE IMPROVEMENT WHEREIN AN AMIDE, IN THE AMOUNT OF AT LEAST 0.25 PART BY WEIGHT PER 100 PARTS BY WEIGHT OF POLYMER, IS ADDED TO THE POLYMER BEFORE ALL OF THE REINFORCING AGENT HAS BEEN ADDED TO THE POLYMER WITH THE PROVISO THAT THE POLYMER CONTAINS LESS THAN 30 PARTS BY WEIGHT OF REINFORCING AGENT PER 100 PARTS BY WEIGHT OF POLYMER WHEN THE AMIDE IS ADDED AND WHEREIN THE AMIDE HAS THE FOLLOWING STRUCTURAL FORMULA:
 2. The vulcanizate prepared by vulcanizing the unvulcanized conjugated diene polymer of claim 1 with an efficient or semi-effIcient sulfur-type vulcanization system.
 3. The unvulcanized conjugated diene polymer prepared according to the process of claim
 1. 4. The process of claim 1 wherein the reinforcing agent is carbon black.
 5. The process of claim 4 wherein the conjugated diene is butadiene-1,3.
 6. The process of claim 5 wherein the polymer is a copolymer containing at least 40 parts by weight of butadiene-1,3 per 100 parts by weight of polymer and as a comonomer a monomer selected from the group consisting of styrene and acrylonitrile.
 7. The process according to claim 1 wherein the amide is N-(4-anilinophenyl)-methacrylamide.
 8. The process according to claim 1 wherein the polymer contains less than 20 parts by weight of reinforcing agent per 100 parts by weight of polymer when the amide is added.
 9. The process according to claim 1 wherein the polymer contains less than 10 parts by weight of reinforcing agent per 100 parts by weight of polymer when the amide is added.
 10. The vulcanizate according to claim 2 wherein the vulcanization system contains 0 to 0.5 part by weight of free sulfur per 100 parts by weight of polymer. 